EP3638553B1

EP3638553B1 - Methods for the assessment of the contamination and the cleaning of a rail, in particular for a railway vehicle

Info

Publication number: EP3638553B1
Application number: EP18740895.0A
Authority: EP
Inventors: Matteo FREA; Luc IMBERT
Original assignee: Faiveley Transport Italia SpA
Current assignee: Faiveley Transport Italia SpA
Priority date: 2017-06-12
Filing date: 2018-06-12
Publication date: 2022-08-31
Anticipated expiration: 2038-06-12
Also published as: US20200101993A1; IT201700064371A1; JP2020523241A; CN110799389A; RU2020100273A; WO2018229638A1; RU2760715C9; RU2760715C2; US11305795B2; HUE060664T2; RU2020100273A3; JP7169307B2; EP3638553A1; ES2931229T3; CN110799389B

Description

Technical sector

The present invention relates to the field of methods for controlling the adhesion value between the wheels of a railway vehicle and a rail. In particular, the invention relates to methods for the assessment of the contamination and cleaning of a rail, in particular, for a railway vehicle.

Prior Art

Electronic systems are installed on board most modern rail vehicles, which typically include wheel skid control subsystems, intended to intervene both when the vehicle is in the traction phase and when it is in the braking phase. These subsystems are known as anti-skid or anti-slide systems, or also WSP (Wheel Slide Protection) systems.
A system for controlling the adhesion of the wheels, as an anti-skid function, according to the prior art, is schematically represented in figure 1 of the accompanying drawings, which refers to a vehicle with n controlled axles A₁, A₂, ..., A_n. The axles A₁, A₂, ..., A_n comprise a respective shaft S₁, S₂, ..., S_n and a respective wheelset W₁, W₂, ..., W_n integral in rotation thereto.
In the drawings, only one wheel of each axle is generally illustrated.
The WSP system of figure 1 comprises an electronic control unit ECU, typically based on a microprocessor architecture that receives tachometer signals relating to the angular velocity of each axle A₁, A₂, ...A_n from detectors SS₁, SS₂, ..., SS_n respectively associated with such axles. The electronic control unit ECU is also connected to the torque control apparatuses TC₁, TC₂, ..., TC_n, each associated with a respective axle A₁, A₂, ..., A_n.
The electronic control unit ECU is arranged to carry out a modulation of the torque applied to each axle according to a predetermined algorithm if, in the case of applying torque during traction or braking in a degraded adhesion situation, the wheels of one or more axles end up in a possible incipient skidding condition. Torque modulation is implemented in such a way as to prevent a total locking of the axles, possibly so as to bring each axle into a situation of controlled sliding with the intention of recovering adhesion and, in any case, for the entire duration of the degraded adhesion situation.
In figure 2, the curves 1, 2 and 3 qualitatively represent the trend of the adhesion according to the ambient conditions: curve 1 corresponds to an adhesion condition in dry contact conditions between the wheels and rails, curve 2 corresponds to an adhesion condition in the presence of moisture between the wheels and rails, and curve 3 represents an adhesion condition in the presence of viscous material between the wheels and rails, such as oil or rotten leaves (typical condition in the autumn period), or even rust mixed with moisture (typical condition in railway depots).
It has been found experimentally that the values of δ at the adhesion peaks a₁, a₂, a₃ vary with the change in the adhesion conditions, moving along a curve as indicated at A in figure 2.
Figure 3 is a diagram illustrating forces applied to an axle's wheel A. From this figure it is clear that: $F_{m} \cdot R = F_{A} \cdot R - J \cdot \dot{ω}$
where: $F_{A} = μ \cdot m \cdot g$
whereby: $F_{m} = μ \cdot m \cdot g - J / R \cdot \dot{ω}$
where F_m is the tangential force applied to a wheel by the traction and/or braking system, R is the radius of the wheel, J is the moment of inertia of the axle, m is the mass resting on the wheel-rail contact point,ω̇ is the instantaneous angular acceleration of the axle.
It is clear that, at the same instantaneous angular acceleration, the maximum applicable force F_m is obtained at the maximum adhesion value µ, i.e. at the points lying on the curve A of figure 2.
If one decides to slide the axle in conditions such as those corresponding, for example, to point b in figure 2, the value of the force F_m available is reduced as a result of the reduction of the adhesion value µ, but an energy injection phenomenon is obtained at the wheel-rail point of contact, proportional to the sliding (difference) between the velocity of the vehicle Vv and the tangential velocity Vr of the wheel, with a power (energy injected per unit of time): $P (δ) = F_{A} (δ) \cdot (V_{v} - V_{r}) = μ (δ) \cdot m \cdot g \cdot (V_{v} - V_{r}) = μ (δ) \cdot m \cdot g \cdot δ \cdot V_{v} .$
The expression (5) above indicates how by increasing δ an increase of the power applied to the wheel-rail contact point is obtained. This injection of energy causes an overheating of the wheel with a consequent cleaning effect of the point of contact, improving the instantaneous adhesion value µ for the next wheel.
It is moreover known that in the case of moisture or rain, significant cleaning effects are obtained, while in the presence of lubricants or rotten leaves, the cleaning effect is less pronounced.
The current systems for recovering adhesion between the wheels and rails impose a fixed sliding value δ, typically between 0.2 and 0.3, the specific value being calibrated in a definitive way during the vehicle approval tests. The selected value of δ is therefore optimized for the type of lubricant used to cause the condition of skidding during the tests, as prescribed, for example, in EN 15595:2009+A1, Railway Applications - Braking - Wheel Slide Protection, para. 6.4.2.1, and is, on the other hand, not optimal for all types of materials that may cause conditions of skidding during the normal service of the vehicle.
The graph of figure 4A shows in a qualitative way how the peak of the global adhesion of a vehicle with four axles varies with the change in δ: bringing all the axles to slide with adhesion corresponding to the value δ₁, as in figure 4A, there is practically no cleaning factor, and therefore the four adhesion curves corresponding to the four wheels substantially coincide with each other and each axle takes advantage of the maximum peak adhesion value µ(δ₁).
If, on the other hand, one brings the axles to slide with an adhesion corresponding to the slide δ₂ as in figure 4B, a high cleaning factor will be obtained: only the µ₁ curve corresponding to the first axle of the vehicle (in the direction of travel) will remain unchanged and equivalent to that of figure 4A, while the curves corresponding to the following axles will have increasing adhesion values due to the cleaning effect achieved by the previous axle. The value µ(δ₂) for each axle is indeed lower than the corresponding value µ(δ₁).
As is qualitatively shown in figure 4C, in the range δ₁ ≤ δ≤ δ₂, a peak average global adhesion value $\overline{μ} = \sum_{1}^{n} μ (δ) / n$
(6) exists.
That which is described above applies, by extension, to a vehicle or train with n axles.
Since the curves which express the adhesion µ as a function of the sliding δ may not be formulated mathematically in an analytical way and vary continuously with the change in the conditions that cause skidding, the geometry of the contact point, and the external ambient conditions, it is not possible a priori, to calculate analytically the optimal sliding value δ.
However, an excellent adhesion control and possible recovery system should be able to analyze the instantaneous adhesion conditions in real time and verify the trend thereof with the change in δ and identify the value of δ such as to maximize $\overline{μ} = \sum_{1}^{n} μ (δ) / n$
. Such value is that which allows the maximum adhesion recovery in case of skidding, which is the value that minimizes the stopping distance in the event of braking in a degraded adhesion condition.
In order to obviate the problems described above, WO 2006/113954 A describes a slide control for railway vehicles, implemented continuously over time, which requires the identification, in optimal adhesion conditions, of the parameters necessary in view of the subsequent desired performance in skid conditions. Such method further requires the overall deceleration of the system to be known.
Furthermore, the process of adjusting the optimum sliding values requires significantly long times. This adjustment process being implemented at the beginning of a skidding phase, i.e. when the vehicle is traveling at high speed, the distance covered by the latter is increased considerably.
In addition, the processes and systems realized according to the prior art are based on the assumption that the wheel adhesion curves are always curves having an adhesion peak µ_p at small sliding values, for example on the order of 1-2%.
In reality, the wheel adhesion curves are not always curves having an adhesion peak µ_p at small sliding values; they may be curves having an adhesion peak µ_p at higher sliding values, such as values on the order of 20-25%.
In this second case, if one erroneously acts as if the curve is a curve having an adhesion peak µ_p at small sliding values, that is, a small sliding value is imposed between the wheels and the rails to obtain peak wheel adhesion, the desired benefit is not achieved. In effect, in small slides, this curve, having an adhesion peak of µ_p at higher sliding values, such as, for example, values on the order of 20-25%, exhibits poor levels of adhesion and poor rail cleaning effects (given that the slide imposed is low).
Therefore, in this second case, the average adhesion value, considering every single adhesion value of the wheels, will not be the optimal one.
EP 2 813 409 A1 describes a method for assessing friction characteristic of a rail based on imposed sliding value between the wheel of a first controlled axle of a rail vehicle and the rail.

Summary of the invention

An object of the present invention is to propose a method for the assessment of the contamination of a rail which allows one to determine the position of the adhesion peak along the adhesion curve of the wheels belonging to a plurality of controlled axles of a vehicle and, consequently, to obtain improved control and possible recovery of the adhesion of the wheels of a controlled axle of a railway vehicle, and to propose a method for assessing the rail cleaning that allows one to propose a better assessment of the cleaning effect among the various successive axles of a railway vehicle.
The aforesaid and other objects and advantages are achieved, according to an aspect of the invention, by a method for the assessment of the contamination of a rail having the features defined in claim 1 and by a method for the assessment of the cleaning of a rail having the features defined in claim 7.
Preferential embodiments of the invention are defined in the dependent claims, the contents of which are intended as an integral and integrating part of the present description.

Brief description of the figures

Further features and advantages of the invention will become apparent from the detailed description that follows, provided purely by way of non-limiting example with reference to the accompanying drawings, wherein:

figure 1 is a block diagram of an anti-skid control system of the wheels of a railway vehicle;
figure 2 is a graph showing qualitatively the trend of the adhesion coefficient µ of the wheels of an axle, shown on the y-axis, as a function of the sliding δ, shown on the x-axis;
figure 3 is a diagram illustrating the forces applied to an axle's wheel;
figures 4A, 4B are graphs showing qualitatively the trends of the adhesion coefficient µ of the wheels of four axles of a vehicle in two different operating conditions;
figure 4C illustrates the trend of an average adhesion curve µ around the peak value;
figure 5 is a graph illustrating an adhesion curve having an adhesion peak at a sliding value lower than the first predetermined threshold;
figure 6 is a graph illustrating an adhesion curve having an adhesion peak at a sliding value greater than the second predetermined threshold;
figure 7 shows four adhesion curves, respectively of wheels belonging to four consecutive axles, in the case wherein there is a cleaning effect of the rail;
figure 8 shows four adhesion curves respectively of wheels belonging to four consecutive axles, in the case wherein the sliding value is imposed to correspond with the adhesion peak between the wheels of the axles and the rail, and consequently there is no cleaning effect of the rail;
figure 9 shows four adhesion curves respectively of wheels belonging to four consecutive axles, in the case wherein the adhesion curve of wheels belonging to a plurality of controlled axles of a railway vehicle exhibits an adhesion peak at a sliding value less than the first predetermined threshold, and the sliding value imposed between the wheels of the axles and the rails is a higher sliding value than the second predetermined threshold; and
figure 10 shows four adhesion curves respectively of wheels belonging to four consecutive axles, in the case wherein the adhesion curves exhibit an adhesion peak at a sliding value greater than the second predetermined threshold and the sliding value imposed between the wheels of the axles and the rails is a higher sliding value than the second predetermined threshold.

Detailed Description

Before describing in detail a plurality of embodiments of the invention, it should be clarified that the invention is not limited in its application to the details of construction or to the configuration of the components provided in the following description or illustrated in the drawings.
As will appear more clearly from the following, the method according to the present invention allows one to determine the position of the adhesion peak along the adhesion curves of the wheels belonging to a plurality of controlled axles of a vehicle, and, consequently, to obtain improved control and possible recovery of the adhesion of the wheels of a controlled axle of a railway vehicle.
Initially referring to adhesion curves such as those in figure 5, the adhesion peak µ_p is obtained for small sliding values on the order of 1-2%.
Defining δ_p as the sliding value for which the adhesion peak µ_p is obtained, it is clear that:

if the axle is brought to slide close to δ_p (small slide), there will be a negligible cleaning effect to the benefit of the local adhesion which assumes the peak value µ_p.
conversely, if the axle is brought to slide at higher sliding values δ, there will be a loss of local adhesion to the benefit of a possible cleaning effect for the following axles. Such effect will be more or less effective depending on the type and amount of contaminant present. The effectiveness of the cleaning is an unknown datum a priori.

Therefore, in order to maximize the average adhesion of the axles, the choice of sliding points at which to make the axles work must generally consider two factors:

1. the benefit of the cleaning on the following axles (increasing as the local sliding increases); and
2. the local adhesion value (decreasing as the sliding increases).

Conversely, in the case of an adhesion curve like that of figure 6, from the literature and the results of experimental tests carried out on rolling stock, it emerges that the trend of the adhesion curves depends on many factors, among which, the type of contaminant, the amount of contaminant, and the weight of the vehicle. Not all adhesion curves necessarily exhibit an adhesion peak µ_p for small sliding values, such as that of figure 5. There are cases wherein the adhesion peak µ_p is obtained for higher sliding values (δ_p ≈ 20%), like the curve in figure 6.
In such case:

if the axle is brought to slide at small sliding values (e.g. δ=1-2%), the cleaning effect will be practically zero and the local adhesion will be reduced with respect to the peak value.
conversely, if the axle is brought to slide at higher values δ (e.g. δ ≈ 20%), there will be a benefit both on the local adhesion and on a possible cleaning effect for the following axles.

In the case of adhesion curves such as those of figure 6, therefore, regardless of the effectiveness of the cleaning, the most appropriate choice is to bring all the axles into large slides (δ ≈ 20% ≈ δ_p) maximizing both the local adhesion and the possible cleaning effect. Based on the above concepts, the method for the assessment of the contamination of a rail, particularly for a railway vehicle, comprises the steps of:

imposing a first sliding value δ₁ lower than a first predetermined threshold t₁ between the wheels W₁ of a first controlled axle A₁ of a railway vehicle and the rail, the first controlled axle A₁ being the head axle of the railway vehicle according to the direction of travel of the railway vehicle;
imposing a second sliding value δ₂ greater than a second predetermined threshold t₂ between the wheels of a second controlled axle A₂ and the rail, the second axle A₂ being the axle following said first axle A₁ according to the direction of travel of the train, and the second predetermined threshold t₂ being greater than said first predetermined threshold t₁;
determining the trend of the adhesion curve between the wheels W belonging to a plurality of controlled axles A_n of the railway vehicle and the rail based on a first adhesion value µ₁ between the wheels of said first axle A₁ and the rail, and a second adhesion value µ₂ between the wheels of said second axle A₂ and the rail.

The step of determining the trend of the adhesion curve between the wheels W belonging to a plurality of controlled axles A_n of the railway vehicle and the rail further comprises the steps of measuring the first adhesion value µ₁ between the wheels of said first axle A₁ and the rail, and the second adhesion value µ₂ between the wheels of said second axle A₂ and the rail;

if the second adhesion value µ₂ is greater than the first adhesion value µ₁, determining that the adhesion curve between the wheels W belonging to the plurality of controlled axles A_n of a railway vehicle and the rail is an adhesion curve having a trend which has an adhesion peak µ_p at a sliding value δ_p greater than the second predetermined threshold t₂; and
if the second adhesion value µ₂ is lower than the first adhesion value µ₁, determining that the adhesion curve between the wheels W belonging to a plurality of controlled axles A_n of a railway vehicle and the rail is an adhesion curve having a trend which has an adhesion peak µ_p at a sliding value δ_p lower than said first predetermined threshold t₁.

By way of example, the first predetermined threshold t₁ may coincide with a sliding value of about 5%, and the first sliding value δ₁ less than the first predetermined threshold between the wheels of a first controlled axle A₁ and a rail may be about 1-2%. The second predetermined threshold t₂ may coincide with a sliding value between about 15% and 25%, and the second sliding value δ₂, greater than the second predetermined threshold between the wheels of at least one second controlled axle A₂ and the rail may be around 20% -25%.
Preferably, the second sliding value δ₂ does not exceed a limit sliding value δ_limit equal to about 25%.
The method for the assessment of the contamination of a rail, if it has been determined that the adhesion curve between the wheels W belonging to a plurality of controlled axles An of a railway vehicle and the rail is an adhesion curve having a trend exhibiting an adhesion peak µ_p at a sliding value greater than the second predetermined threshold t₂, may comprise the step of:

imposing a sliding value δ greater than the second predetermined threshold t₂ between the wheels of all controlled axles and the rail.

On the other hand, the method for assessing the contamination of a rail, if it has been determined that the adhesion curve between the wheels W belonging to the plurality of controlled axles A_n of a railway vehicle and the rail is an adhesion curve having a trend which has an adhesion peak µ_p at a sliding value δ_p less than the first predetermined threshold t₁, may comprise the step of:

calculating the value of the adhesion difference Δµ_slide by means of the difference between the first adhesion value µ₁ and the second adhesion value µ₂;
imposing the second sliding value δ₂ greater than a second predetermined threshold t₂ between the wheels of at least one third axle A₃ and the rail, the third axle A₃ being the axle following said second axle A₂ according to the direction of travel of the train;
calculating the value of the adhesion difference Δµ_clean generated by the cleaning effect of the wheels of the second axle A₂ to the benefit of the wheels of the third axle A₃, said value of the adhesion difference Δµ_clean generated by the cleaning effect being obtained by means of the difference between the adhesion value µ₃ between the wheels of the third axle A₃ and the rail, and the adhesion value µ₂ between the wheels of the second axle A₂ and the rail;

if the value of the adhesion difference Δµ_clean generated by the cleaning effect of the wheels is predominant with respect to the value of the adhesion difference Δµ_slide multiplied by an adaptive factor Fad, the value of which is inversely proportional to the number of axles, imposing a sliding value δ greater than the second predetermined threshold t₂ between the wheels W of all the controlled axles A₁, ..., A_n and the rail;
if the value of the adhesion difference Δµ_clean generated by the cleaning effect of the wheels is not predominant with respect to the value of the adhesion difference Δµ_slide multiplied by an adaptive factor F_ad the value of which is inversely proportional to the number of axles, imposing a sliding value δ lower than the first predetermined threshold ti between the wheels W of all the controlled axles A₁, ..., A_n and the rail.

The method for the assessment of the contamination of a rail, if it has been determined that the adhesion curve of the wheels W belonging to a plurality of controlled axles A_n of a railway vehicle is an adhesion curve having an adhesion peak µ_p at a sliding value δ_p less than the first predetermined threshold t₁, may comprise the step of:

after having imposed a sliding value δ₂ greater than the second predetermined threshold t₂ between the wheels of all the controlled axles A₁, ..., A₀ and the rail, due to the non-predominance of the value of the adhesion difference Δµ_clean generated by the cleaning effect of the wheels with respect to the value of the adhesion difference Δµ_slide multiplied by an adaptive factor F_ad the value of which is inversely proportional to the number of axles, if the adhesion value µ_n of the wheels of a previous axle An is coincident with the adhesion value µ_n+1 of the wheels of the next axle A_n+1, imposing a first sliding value δ₁ lower than the first predetermined threshold t₁ between the wheels of at least one following axle A_n+1, A_n+2, ... and the rail.

Due to this last step described above, it may be noted that the cleaning effect of the rail that was exhibited in the first axles according to the direction of travel no longer involves an increase in adhesion for the following axles (for example, because now the rail is completely clean), and consequently, it is appropriate to impose on the following axles the sliding value corresponding to the adhesion peak and not a sliding value useful for cleaning the rail.
By way of example, considering the second axle as the previous axle A_n and the third axle as the following axle A_n+1, after having imposed a sliding value δ₂ greater than the second predetermined threshold t₂ between the wheels of all the controlled axles and the rail, due to the non-predominance of the value of the adhesion difference Δµ_clean generated by the cleaning effect of the wheels with respect to the value of the adhesion difference Δµ_slide multiplied by an adaptive factor Fad, a first sliding value δ₁ may be imposed less than the first predetermined threshold t₁ between the wheels of the axles following the third and the rail, if the adhesion value µ₂ of the wheels of the second axle A₂ (previous axle A_n) coincides with the adhesion value µ₃ of the wheels of the third axle (following axle A_n+1).
By way of example, the method for assessing the contamination of a rail may be repeated after a predetermined time interval (for example every 30 seconds) or it may be repeated after a predetermined distance has been traveled by the railway vehicle.
The invention comprises moreover a method for assessing the cleaning of a rail for a railway vehicle, comprising the steps of:

imposing a first sliding value δ₁ lower than a first predetermined threshold t₁ between the wheels W₁ of a first controlled axle A₁ of a railway vehicle and the rail; the first controlled axle A₁ being the head axle of the railway vehicle according to the direction of travel of the railway vehicle;
imposing a second sliding value δ₂ greater than a second predetermined threshold t₂ between the wheels of a second controlled axle A₂ and the rail, the second axle A₂ being the axle following said first axle A₁ according to the direction of travel of the train, and said second predetermined threshold t₂ being greater than said first predetermined threshold t₁;
imposing a third sliding value δ₃ equal to said second sliding value δ₂ between the wheels of a controlled third axle A₃ and the rail, the third axle A₃ being the axle following said second axle A₂ according to the direction of travel of the train;
determining the effectiveness of the cleaning of the rail generated by the sliding of the second axle A₂ to the benefit of the third axle A₃ based on a first adhesion value µ₂ between the wheels of said second axle A₂ and the rail and a second adhesion value µ₃ between the wheels of said third axle A₃ and the rail.

The aforesaid step of determining the effectiveness of the cleaning of the rail further comprises the steps of:

measuring the first adhesion value µ₂ and the second adhesion value µ₃; and
determining the effectiveness of the cleaning by performing a subtraction operation between the second adhesion value µ₃ and the first adhesion value µ₂.

In the following is reported by way of example, an illustrative case wherein the total number of axles of the railway vehicle is four.
Considering figure 7, it is possible to assess the adhesion engaged by the four axles making up the railway vehicle.
The adhesion µ₁ available for the first axle A₁ is not influenced by the cleaning, such axle being the first to encounter the rail. The adhesion µ₁ depends only on the conditions of the rail, i.e. the ambient/contaminant conditions that will be indicated in the following with "amb".
The adhesion µ₁ engaged by the first axle will then be a function of the local sliding δ₁ of the first axle on the rail: $μ_{1} = f (μ_{\max}, δ, _{1}) = f (amb, δ_{1})$
Conversely, the adhesion µ₂ available for the second axle depends on the cleaning produced by the previous first axle (Δµ₁₂). $μ_{2, \max} = μ_{\max} + {Δμ}_{12}$
The cleaning produced by the first axle in favor of the second axle Δµ₁₂ is a function of the sliding δ₁ of the first axle on the rail, as well as the cleaning characteristics typical of the contaminant (contaminant more or less easy to remove with the same sliding), which are indicated hereinafter with the term "cleaning". $μ_{2, \max} = μ_{\max} + f (clean, δ, _{1})$
The adhesion µ₂ engaged by the second axle will then be a function of the local sliding δ₂ of the second axle on the rail. $μ_{2} = f (μ) (_{2, \max}, δ, _{2}) = f (amb, δ_{1}, cleaning, δ, _{2})$
Likewise, the adhesion µ₃ engaged by the third axle depends on the local sliding δ₃ and on the cleaning produced by the previous axles, hence by δ₁, δ₂ and by cleaning.
Likewise, the adhesion µ₄ engaged by the fourth axle depends on the local sliding δ₄ and on the cleaning produced by the previous axles, hence by δ₁, δ₂, δ₃ and by the cleaning.
According to these considerations: $μ_{average} = \frac{1}{4} * (\begin{array}{l} f (amb, δ) (_{1}) + f (amb, δ_{1}, δ_{2}, cleaning) + f (amb, δ_{1}, δ_{2}, δ_{3}, cleaning) \\ + f (amb, δ_{1}, δ_{2}, δ_{3}, δ_{4}, cleaning) \end{array})$
In the case of an adhesion curve such as the one illustrated in figure 5, and in the case wherein a sliding corresponding to the adhesion peak µ_p is imposed on all the axles, assuming (see figure 8) control of all axles on the adhesion peak µ_p, that is, at small slides around δ_p, no rail cleaning is produced. ${Δμ}_{12} = {Δμ}_{23} = {Δμ}_{34} = 0$
and therefore $μ_{2, \max} = μ_{3, \max} = μ_{4, \max} = μ_{1, \max}$
All the axles thus find the same adhesion as the head axle finds (first axle in the direction of travel), as no axle cleans the rail.
Thus: $μ_{average} = μ_{1, \max}$
In the case of an adhesion curve such as that of figure 5, wherein on all the axles a slide of δ >> δp is imposed, it is possible to obtain a cleaning effect (this effect is certainly not a priori but rather depends on the effectiveness of the cleaning on the contaminant in question: parameter previously defined as cleaning).
With reference to figure 9: ${Δμ}_{12} = {Δμ}_{23} = {Δμ}_{34} = {Δμ}_{clean}$
Therefore: $μ_{2, \max} = μ_{1, \max} + {Δμ}_{clean}$
$μ$ $_{3, \max} = μ_{2, \max} + {Δμ}_{clean} = μ_{1, \max} + 2 * {Δμ}_{clean}$
$μ$ $_{4, \max} = μ_{3, \max} + {Δμ}_{clean} = μ_{1, \max} + 3 * {Δμ}_{clean}$
At the same time, each axle, sliding at a δ far from the peak value δ_p, will not exploit all the locally available adhesion µ.
With reference to figure 9: $μ_{1} = μ_{1, \max} - {Δμ}_{slide}$
$μ$ $_{2} = μ_{2, \max} - {Δμ}_{slide} = {Δμ}_{1, \max} + {Δμ}_{clean} - {Δμ}_{slide}$
$μ$ $_{3} = μ_{3, \max} - {Δμ}_{slide} = {Δμ}_{1, \max} + 2 * {Δμ}_{clean} - {Δμ}_{slide}$
$μ$ $_{4} = μ_{4, \max} - {Δμ}_{slide} = {Δμ}_{1, \max} + 3 * {Δμ}_{clean} - {Δμ}_{slide}$
Calculating the average adhesion of the vehicle: $μ_{average} = μ_{1, \max} + \frac{3}{2} * {Δμ}_{clean} - {Δμ}_{slide}$
Comparing the average adhesion obtained in the case of an adhesion curve such as the one illustrated in figure 5, in the case wherein on all the axles a slide corresponding to the adhesion peak is imposed, and in the case wherein on all the axles a slide of δ >> δ_p is imposed, one notes that:

If ${Δμ}_{clean} > \frac{2}{3} * {Δμ}_{slide}$
, it is appropriate to control the axles in large slides of δ >> δ_p, i.e. with a slide greater than the second predetermined threshold t₂.
If ${Δμ}_{clean} < \frac{2}{3} * {Δμ}_{slide}$
, it is appropriate to control the axles with reduced sliding δ = δ_p, i.e. with a slide less than the first predetermined threshold t₁.

In the examples given above, the adaptive factor is equal to 2/3. For example, in the case of five axles, the adaptive factor is equal to 1/2.
In the case of adhesion curves such as those of figure 6, regardless of the effectiveness of cleaning, the most appropriate choice is to bring all the axles into large slides, that is, with a slide greater than the second predetermined threshold t₂ (δ ≈ 20% ≈ δ _p) consequently maximizing both the local adhesion and the possible cleaning effect.
According to such management of the sliding points we have (see figure 10): $μ_{1} = μ_{1, \max}$
$μ$ $_{2} = μ_{1, \max} + {Δμ}_{clean}$
$μ$ $_{3} = μ_{1, \max} + 2 * {Δμ}_{clean}$
$μ$ $_{4} = μ_{1, \max} + 3 * {Δμ}_{clean}$
Thus, the average vehicle-level adhesion is: $μ_{average} = μ_{1, \max} + \frac{3}{2} * {Δμ}_{clean}$
From the analysis of the preceding cases, (case of an adhesion curve such as the one illustrated in figure 5 and wherein on all the axles a slide is imposed corresponding to the adhesion peak, the case of an adhesion curve such as the one of figure 5 wherein on all the axles a slide of δ >> δ_p is imposed, and the case of adhesion curves such as those in figure 6), it may be noted that the choice of the optimal sliding point (the one that maximizes the average adhesion of the vehicle) must pass through the assessment of three main factors:

FACTOR 1: Type of adhesion curve: i.e. if the adhesion peak is obtained for small sliding values (figure 5), i.e. for a slide less than the first predetermined threshold t₁, or for large sliding values (figure 6), i.e. for a slide greater than the second predetermined threshold t₂, close to δ_limit;
FACTOR 2: Δµ_slide (parameter defined only for the curve illustrated in figure 5), i.e. difference in adhesion between the peak of the curve and the adhesion engaged with a slide close to the limit slide (see figure 9).
FACTOR 3: Δµ_clean, i.e. the effectiveness of the cleaning effect from which the axle (n+1) benefits when the axle n is made to slide with a slide greater than the second predetermined threshold t₂, close to δ_limit.

In the case of a railway vehicle moving on rails, the assessment of these three factors and the consequent choice of the sliding point, according to the criteria described above, must take place in real time during the braking of the vehicle in order to maximize the average adhesion engaged by the vehicle, thereby maximizing the deceleration of the vehicle and thereby minimizing the stopping distance of the vehicle.
To assess the effectiveness of cleaning (FACTOR 3) it is therefore necessary to impose a significant slide, i.e. a slide greater than the second predetermined threshold t₂ (δ ≈ δ_limit) on the axle n and to verify the potential gain of adhesion on the axle (n+1).
At the same time, by sliding the axle with a slide greater than the second predetermined threshold t₂, close to δ_limit, the rail conditions are modified for the following axles and it becomes impossible to assess the adhesion value relative to small slides, i.e. with a slide less than the first predetermined threshold t₁ (δ <5%). Therefore, factors 1 and 2 cannot be assessed.
The object of the invention is to manage the sliding of the vehicle axles as follows:

FIRST AXLE: δ1 ≈ 1-2%
SECOND AXLE: δ₂ ≈ 20%
THIRD AXLE: δ₃ = δ₂ ≈ 20%
FOURTH AXLE: optional

The first axle, the head axle, is controlled in a small slide. In this way, by measuring the adhesion engaged by the first axle, the adhesion value relative to small slides is obtained $μ_{1} = μ (1 - 2 %)$
without producing cleaning, i.e. without changing the characteristics of the rail for following axles.
The second axle, on the other hand, is controlled in a significant slide, i.e. greater than the second predetermined threshold t₂. In this way, by measuring the adhesion engaged by the second axle, the adhesion value relative to large slides is obtained $μ_{2} = μ (20 %)$
producing a possible cleaning for the following axle, cleaning that will depend on the characteristics of the contaminant (cleaning factor 3).
The third axle is controlled at the same sliding value imposed for the second axle.
In this way, by measuring the adhesion engaged by the third axle, it is possible to assess the effectiveness of the cleaning by calculating the cleaning factor: ${Δμ}_{clean} = μ_{3} - μ_{2}$
Moreover, by comparing the measured adhesion for the first and second axles, the type of adhesion curve may be determined (FACTOR 1) and possibly Δµ_slide (FACTOR 2) may calculated.
If (µ₂> µ₁), it is a case of an adhesion curve of the type illustrated in figure 6.
The most appropriate choice is therefore that of bringing all the axles into large slides, that is to say, a sliding greater than the second predetermined threshold t₂ (δ ≈ 20% ≈ δ_limit);
If (µ₂> µ₁), it is a case of an adhesion curve of the type illustrated in figure 5) and one may calculate: ${Δμ}_{slide} = μ_{1} - μ_{2}$
At this point, noting all the factors, one may choose the optimal sliding point: $If ({Δμ}_{clean} > \frac{2}{3} * {Δμ}_{slide}) :$
the most appropriate choice is therefore that of bringing all the axles into large slides, that is to say, a slide greater than the second predetermined threshold t₂ (δ ≈ 20% ≈ δ_limit); $if ({Δμ}_{clean} < \frac{2}{3} * {Δμ}_{slide}) :$
the most appropriate choice is to control the axles on the adhesion peak, i.e. with a slide less than the first predetermined threshold t₁ (δ < 5%).
Naturally, without altering the principle of the invention, the embodiments and the details of implementation may vary widely with respect to those described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the appended claims.

Claims

A method for the assessment of the contamination of a rail, in particular for a railway vehicle, comprising the steps of:
- imposing a first sliding value (δ₁) lower than a first predetermined threshold (t₁) between the wheels (W₁) of a first controlled axle (A₁) of a rail vehicle and the rail, the first controlled axle (A₁) being the head axle of the railway vehicle according to the direction of travel of the railway vehicle;

- imposing a second sliding value (δ₂) greater than a second predetermined threshold (t₂) between the wheels of a second controlled axle (A₂) and the rail, the second axle (A₂) being the axle following said first axle (A₁) according to the direction of travel of the train, and the second predetermined threshold (t₂) being greater than said first predetermined threshold (ti);

- determining the trend of the adhesion curve between the wheels (W) belonging to a plurality of controlled axles (A_n) of the railway vehicle and the rail, based on a first adhesion value (µ₁) between the wheels of said first axle (A₁) and the rail, and a second adhesion value (µ₂) between the wheels of said second axle (A₂) and the rail;
wherein said step of determining the trend of the adhesion curve between the wheels (W) belonging to a plurality of controlled axles (A_n) of a railway vehicle and the rail comprises the steps of:
- measuring the first adhesion value (µ₁) between the wheels of said first axle (A₁) and the rail, and the second adhesion value (µ₂) between the wheels of said second axle (A₂) and the rail;

- if the second adhesion value (µ₂) is greater than the first adhesion value (µ₁), determining that the adhesion curve between the wheels (W) belonging to the plurality of controlled axles (A_n) of a railway vehicle and the rail is an adhesion curve having a trend which has an adhesion peak (µ_p) at a sliding value (δ_p) greater than the second predetermined threshold (t₂); and

- if the second adhesion value (µ₂) is lower than the first adhesion value (µ₁), determining that the adhesion curve between the wheels (W) belonging to a plurality of controlled axles (A_n) of a railway vehicle and the rail is an adhesion curve having a trend which has an adhesion peak (µ_p) at a sliding value (δ_p) lower than said first predetermined threshold (t₁).
A method for the assessment of the contamination of a rail according to claim 1, wherein:
a) if it has been determined that the adhesion curve between the wheels (W) belonging to a plurality of controlled axles (A_n) of a railway vehicle and the rail is an adhesion curve having a trend which has an adhesion peak (µ_p) at a sliding value greater than the second predetermined threshold (t₂), said method comprises the step of:
- imposing a sliding value (δ) greater than the second predetermined threshold (t₂) between the wheels of all controlled axles and the rail;

b) if it has been determined that the adhesion curve between the wheels (W) belonging to the plurality of controlled axles (A_n) of a railway vehicle and the rail is an adhesion curve having an adhesion peak (µ_p) at a sliding value (δ_p) lower than the first predetermined threshold (t₁), said method further comprises the steps of:
- calculating the value of the adhesion difference (Δµ_slide) by means of the difference between the first adhesion value (µ₁) and the second adhesion value (µ₂);

- imposing the second sliding value (δ₂) greater than a second predetermined threshold (t2) between the wheels of at least one third axle (A₃) and the rail; the third axle (A₃) being the axle following said second axle (A₂) according to the direction of travel of the train;

- calculating the value of the adhesion difference (Δµ_clean) generated by the cleaning effect of the wheels of the second axle (A₂) to the benefit of the wheels of the third axle (A₃); said value of the adhesion difference (Δµ_clean) generated by the cleaning effect being obtained by means of the difference between the adhesion value (µ₃) between the wheels of the third axle (A₃) and the rail, and the adhesion value (µ₂) between the wheels of the second axle (A₂) and the rail;

- if the value of the adhesion difference (Δµ_clean) generated by the cleaning effect of the wheels is predominant with respect to the value of the adhesion difference (Δµ_slide) multiplied by an adaptive factor (F_ad) the value of which is inversely proportional to the number of axles, imposing a sliding value (δ) greater than the second predetermined threshold (t₂) between the wheels (W) of all controlled axles (A₁, ..., A_n) and the rail;

- if the value of the adhesion difference (Δµ_clean) generated by the cleaning effect of the wheels is not predominant with respect to the value of the adhesion difference (Δµ_slide) multiplied by an adaptive factor (F_ad) the value of which is inversely proportional to the number of the axles, imposing a sliding value (δ) lower than the first predetermined threshold (t₁) between the wheels (W) of all controlled axles (A₁, ..., A_n) and the rail.
A method for the assessment of the contamination of a rail according to claim 2, wherein if it has been determined that the adhesion curve of the wheels (W) belonging to a plurality of controlled axles (A_n) of a railway vehicle is an adhesion curve having an adhesion peak (µ_p) at a sliding value (δ_p) lower than the first predetermined threshold (t₁), said method further comprises the step of:
- after having imposed a sliding value (δ₂) greater than the second predetermined threshold (t₂) between the wheels of all controlled axles (A₁, ..., A_n) and the rail, due to the non-predominance of the value of the adhesion difference (Δµ_clean) generated by the cleaning effect of the wheels with respect to the value of the adhesion difference (Δµ_slide) multiplied by an adaptive factor (F_ad) the value of which is inversely proportional to the number of axles, if the adhesion value (µ_n) of the wheels of a previous axle (A_n) is coincident with the adhesion value of the wheels of the next axle, imposing a first sliding value (δ₁) lower than the first predetermined threshold (t₁) between the wheels of at least one following axle and the rail.
A method for the assessment of the contamination of a rail according to any of the preceding claims, wherein the method for the assessment of the contamination of a rail is repeated after a predetermined time interval.
A method for the assessment of the contamination of a rail according to any one of claims 1 to 3, wherein the method for the assessment of the contamination of a rail is repeated after a predetermined distance has been traveled by the rail vehicle.
A method for the assessment of the contamination of a rail according to any of the preceding claims, wherein the first predetermined threshold (t₁) has a sliding value lower than 5%, and the second predetermined threshold (t₂) has a sliding value between 15% and 25%.
A method for the assessment of the cleaning of a rail for a railway vehicle, comprising the steps of:
- imposing a first sliding value (δ₁) lower than a first predetermined threshold (t₁) between the wheels (W₁) of a first controlled axle (A₁) of a rail vehicle and the rail, the first controlled axle (A₁) being the head axle of the railway vehicle according to the direction of travel of the railway vehicle;

- imposing a second sliding value (δ₂) greater than a second predetermined threshold (t₂) between the wheels of a second controlled axle (A₂) and the rail; the second axle (A₂) being the axle following said first axle (A₁) according to the travel direction of the train, and said second predetermined threshold (t₂) being greater than said first predetermined threshold (ti);

- imposing a third sliding value (δ₃) equal to said second sliding value (δ₂) between the wheels of a controlled third axle (A₃) and the rail; the third axle (A₃) being the axle following said second axle (A₂) according to the travel direction of the train;

- determining the effectiveness of the cleaning of the rail generated by the sliding of the second axle (A₂) to the benefit of the third axle (A₃) based on a first adhesion value (µ₂) between the wheels of said second axle (A₂) and the rail and a second adhesion value (µ₃) between the wheels of said third axle (A₃) and the rail;
wherein the step of determining the effectiveness of the cleaning of the rail comprises the steps of:
- measuring the first adhesion value (µ₂) and the second adhesion value (µ₃); and

- determining the effectiveness of the cleaning by performing a subtraction operation between the second adhesion value (µ₃) and the first adhesion value (µ₂).